create missing directory when creating package init file (#34)

diff --git a/extract_wheels/lib/namespace_pkgs.py b/extract_wheels/lib/namespace_pkgs.py
index 266b953..3a1b33d 100644
--- a/extract_wheels/lib/namespace_pkgs.py
+++ b/extract_wheels/lib/namespace_pkgs.py
@@ -84,6 +84,8 @@
 
     if os.path.isfile(ns_pkg_init_filepath):
         raise ValueError("%s already contains an __init__.py file." % dir_path)
+    if not os.path.exists(dir_path):
+        os.makedirs(dir_path)
     with open(ns_pkg_init_filepath, "w") as ns_pkg_init_f:
         # See https://packaging.python.org/guides/packaging-namespace-packages/#pkgutil-style-namespace-packages
         ns_pkg_init_f.write(
diff --git a/extract_wheels/lib/namespace_pkgs_test.py b/extract_wheels/lib/namespace_pkgs_test.py
index d4e2a4c..056bb4d 100644
--- a/extract_wheels/lib/namespace_pkgs_test.py
+++ b/extract_wheels/lib/namespace_pkgs_test.py
@@ -131,5 +131,13 @@
         self.assertEqual(actual, set())
 
 
+class TestaddPkgutilStyleNamespacePkgInit(unittest.TestCase):
+    def test_missing_directory_is_created(self):
+        directory = TempDir()
+        missing_directory = pathlib.Path(directory.root()) / "missing_directory"
+        namespace_pkgs.add_pkgutil_style_namespace_pkg_init(str(missing_directory))
+        self.assertTrue(missing_directory.is_dir())
+
+
 if __name__ == "__main__":
     unittest.main()